(1) Field of the Invention
The instant invention relates to underwater acoustic sensor systems and more particularly to a reinforced foam core acoustic baffle for use at depths up to 1200 feet.
(2) Description of the Prior Art
It is well known in the art to provide underwater noise measurement, tracking and telemetry systems with acoustic baffles in order to reduce underwater background noise such as that caused by wave motion, wind, and electro-mechanical machinery on boats. In this regard, pressure-release foam baffles have heretofore been known in the art for use in shallow water acoustic sensor systems. Pressure-release foam is a low-density foam having a high content of air pockets and therefore it greatly dampens any sound pressure wave impinging on it. However, it has been found that pressure-release foam is not useful in depths greater than 300 feet because hydrostatic pressure crushes the foam. Denser foams are able to withstand greater pressure; however, they also have poorer acoustic baffling capabilities.
A deep water acoustic baffle is disclosed in the U.S. Pat. No. 4,975,799 to McGee et al. It comprises a one-inch thick sheet of fiber-metal which is enclosed in neoprene. While this baffle is highly stable at deep water pressures, the material in general is inferior to low-density pressure-release foam in its ability to provide acoustic baffling.
Also of interest is U.S. Pat. No. 4,669,573 to Goodman which discloses an underwater acoustic baffle enhancer. The '573 baffle enhancer comprises a stiffened resistive screen fixed in front of a compliant material. An irregular shaped material is provided on the other side of the screen to provide stiffness. The core of the baffle is suffused with water to prevent collapse of the baffle under large hydrostatic pressures.
Other acoustic baffles for use in depths of up to two thousand feet comprise laminated structures which include a rigid inner element sandwiched between two flexible outer sheets and surrounded around its edges with a waterproof seal to completely encapsulate the inner element. The inner element includes a plurality of evenly distributed air cavities which provide a low acoustic impedance compared to water. The inner element further maintains a constant separation between the flexible cover sheets, and therefore maintains a low acoustic impedance even under high hydrostatic pressures.
Although thee prior art structures can provide a low acoustic impedance at great depths, they are considered to be too costly and too heavy for use in current systems.